This invention relates to a new electronic governor for controlling and stabilizing the electrical power output delivered to an output circuit by an AC alternator having a rotating shaft driven by a source. The invention is applicable for both variable and steady sources of power including diesel engines and small scale hydro. It provides fast response to short term fluctuations while at the same time providing long term stability and accuracy.
Conventional governors detect and respond to changes in speed or angular velocity of the alternator or generator drive shaft. A governor, which is based upon changes in speed or angular velocity derived from a shaft detector, can react only after there has been measurable inertial change in the mass of the rotating machinery. This flywheel effect produces a slow response time in conventional governors necessarily extending over many cycles of the rotating shaft.
Typical governors operate on mechanical principles for stabilizing the mechanical speed or angular velocity of the generator or alternator shaft. More recently, electronic load governors have been introduced, but such electronic governors are based upon detecting and maintaining constant system frequency. Because such governors are based on the frequency of the output, the response time is again limited. The frequency of the output reflects the speed of rotation or angular velocity of the shaft, and changes in frequency are detected only after the delay of inertial effects as mechanical changes take place in the shaft speed rotation.
Thus, J. L. Woodward and J. T. Boys describe a "Digital Electronic Load Governor For Small Hydro Plants" in the July, 1980, issue of Water Power and Dam Construction. The electronic controller described by Woodward and Boys uses the observed frequency at the terminals to maintain constant system frequency. This electronic controller reacts more quickly than a mechanical governor after a frequency change is observed. However, it is still limited by the delay in observing measurable frequency changes introduced by the inertia of the rotating machinery and phase shift noise on the alternator output. To applicant's knowledge, this is true of other attempts at electronic load control governing such as, for example, referred to by R. J. Armstrong--Evans in "Micro-Hydro as an Appropriate Technology in Developing Countries" found in Water Power '79 Abstracts of the International Conference on Small Scale Hydro, Oct. 1-3, 1979, sponsored by the U.S. Army Corp of Engineers and the U.S. Department of Energy. The foregoing works from New Zealand and England introduce the use of dummy loads and governing by coupling and uncoupling such loads across the output terminals for maintaining a specified load level. However, such governors respond to changes in frequency output and therefore to mechanical changes in speed or angular velocity, with inherent limitations in response time.
The closest United States patent of which applicant is aware is the Lydick U.S. Pat. No. 3,546,533. This patent describes a protective device designed to take drastic action by cutting out loads in an electrical power system. The Lydick device is frequency responsive and therefore responds only after inertial changes in speed of rotation. It operates at a high deviation threshold of measured frequency from a standard frequency and can provide only a fixed quantum load change in response to a deviation exceeding the threshold. Lydick makes no provision for switching loads back into the system and is intended for emergency blackout and brownout situations.